1. Field of the Invention
This invention relates to a method for making an expanded shoe sole, more particularly to a method for making an expanded shoe sole that includes a first sole part and a second sole part which is inlaid in the first sole part.
2. Description of the Related Art
FIGS. 1 and 2 illustrate how a shoe sole 6 is prepared in a mold 3 according to a conventional method. The shoe sole 6 includes a first sole part 61 and a second sole part 62 that is inlaid in the first sole part 61. The method includes the steps of placing an unexpanded sole blank 1 in the mold 3 which is heated to a molding temperature, and filling and thermally molding a foamable material in the mold 3. In order to prevent warping of the unexpanded sole blank 1 by virtue of reaction for expansion and cross-linking during the aforesaid molding process, a limiting member 2, which is in the form of an unexpanded sole blank 1 by means of ribs 404 formed on an inner wall of the mold 3. The limiting member 2 melts in the mold 3 during the molding process, and cooperates with the foamable material to form the first sole part 61. The unexpanded sole blank 1 undergoes the reaction for expansion and cross-linking to form the second sole art 62. The aforesaid conventional method is disadvantageous in that, since the unexpanded sole blank 1 is in direct contact with the mold 3, which is at the molding temperature, the temperature of the unexpanded sole blank 1 will be rapidly raised to the molding temperature, and the unexpanded sole blank 1 will warp by virtue of the reaction for expansion and cross-linking prior to the filling of the foamable material in the mold 3, which, in turn, results in dismounting of the limiting member 2 from the ribs 404 and poor quality of the resulting shoe sole 6. Moreover, since the ribs 404 are at the molding temperature, the operator may be injured by the ribs 404 during the mounting of the limiting member 2 thereon.
Therefore, the object of the present invention is to provide a method for making an expanded shoe sole that is capable of overcoming the aforementioned drawbacks of the prior art.
According to the present invention, there is provided a method for making an expanded shoe sole that includes a first sole part and a second sole part which is inlaid in the first sole part. The method comprises the steps of: (a) molding a first foamable material to form an unexpanded sole blank, and cooling the unexpanded sole blank to harden the unexpanded sole blank; (b) positioning the hardened unexpanded sole blank on a first mold; (c) heating a second mold to a molding temperature; (d) positioning assembly of the hardened unexpanded sole blank and the first mold in a mold cavity in the second mold heated in the step (c) in such a manner that the hardened unexpanded sole blank is separated from the second mold by the first mold and that the first mold increases the conductive resistance for heat to transfer from the second mold to the hardened unexpanded sole blank; (d) filling a second foamable material to surround the hardened unexpanded sole blank on the first mold in the mold cavity prior to expansion and cross-linking of the hardened unexpanded sole blank; and (e) thermally molding the second foamable material and the hardened unexpanded sole blank in the second mold at the molding temperature to permit the second foamable material and the hardened unexpanded sole blank to undergo reaction for expansion and cross-linking to form the first and second sole parts of the expanded shoe sole, respectively.